Rifted continental margins and extensional basins, provide lasting records of the processes that occur during continental break-up and initial spreading. The eastern Black Sea (EBS) basin provides a good setting to study the development of continental margins, because of ongoing sedimentation during its development and the close proximity of its conjugate margins. Here, I present an analysis of a new wide-angle seismic dataset that reveals the structure of the deep sediments, crust and upper mantle within the EBS basin. These data provide a unique look at the formation of extensional basins, as the dataset includes a prole that is orientated parallel to the rift axis. This prole places new constraints on the variation in magmatism that accompanied continental rifting and the lateral extent over which these variations occur. The wide-angle data show 8-9km of sediment in the centre of the basin, and reveal a wide-spread low-velocity zone (LVZ) within the deep sediments. The depth of this LVZ coincides with the organic-rich mud layer identied as the Maikop, and indicates overpressure within this formation. From the seismic velocity model, excess pore pressures of 60 - 70 MPa above hydrostatic were estimated within the Maikop. The wide-angle data also reveal highly thinned continental crust (7km thick) in the western EBS, and crust interpreted as thick oceanic crust (13km thick) in the eastern EBS, implying a transition from magma-starved to magmatically robust rifting. Lateral variations in mantle temperature and composition can account for a gradual increase in magmatism, but the wide-angle data reveal that this transition is abrupt (30km) and coincides with one of a series of basement scarps. These results impact the interpretations of other rift zones, where a variation in the syn-rift magmatism is observed, but the nature of the transition is not known.